Various dehydrogenation processes have been proposed to dehydrogenate dehydrogenatable hydrocarbons such as cyclohexanone and cyclohexane. For example, these dehydrogenation processes have been used to convert at least a portion of the cyclohexanone into phenol.
Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone.
Other known routes for the production of phenol involve the direct oxidation of benzene, the oxidation of toluene, and the oxidation of s-butylbenzene wherein methyl ethyl ketone is co-produced with phenol in lieu of acetone produced in the Hock process.
Additionally, phenol can be produced by the oxidation of cyclohexylbenzene to cyclohexylbenzene hydroperoxide wherein cyclohexanone is co-produced with phenol in lieu of acetone produced in the Hock process. A producer using this process may desire to dehydrogenate at least a portion of the cyclohexanone produced into additional phenol depending on market conditions.
There are many methods for dehydrogenating various compounds into phenol. For example, U.S. Pat. No. 4,933,507 discloses that phenol can be produced by dehydrogenating cyclohexenone through a vapor-phase reaction in the presence of hydrogen using a solid-phase catalyst having platinum and an alkali metal carried on a support such as silica, silica-alumina or alumina. In addition, Saito et al. disclose the use of palladium supported on various metal oxides (Al2O3, TiO2, ZrO2, MgO) as a catalyst in the dehydrogenation of cyclohexanone to phenol. See “Performance of Activity Test on Supported Pd Catalysts for Dehydrogenation of Cyclohexanone to Phenol (effect of supports on activity),” Ibaraki Kogyo Koto Senmon Gakko Kenkyu Iho (1995), 30, pp. 39-46.
One problem that has been encountered in the use of dehydrogenation catalyst compositions in the dehydrogenation of dehydrogenatable compounds such as cyclohexanone is that the activity of the dehydrogenation component, such as a noble metal, decreases fairly rapidly. Accordingly, there is a need for a cyclohexanone dehydrogenation catalyst having improved resistance to deactivation.
According to the present invention, it has now been found that the stability of a dehydrogenation catalyst may be improved by operating dehydrogenation process at a pressure above 50 psig (345 kPag).